On April 20th, the latest Ubuntu release, Ubuntu 23.04 (Lunar Lobster) was released. In keeping with all Ubuntu releases since 2016, this one is supported in Linux on IBM zSystems and LinuxONE. General release notes for Ubuntu 23.04 are available here: Lunar Lobster Release Notes and a blog post by Frank Heimes, Technical Lead for Ubuntu on IBM zSystems and LinuxONE at Canonical details the components specific to s390x in the Ubuntu on Big Iron Blog: Today Ubuntu 23.04 (Lunar Lobster) got released!
As with the previous release, this version contains support for the IBM z16 and LinuxONE Emperor 4 and Rockhopper 4, including the new rack-mount systems released earlier this month.
It contains various updated software libraries and a new kernel, new versions of s390-tools and openCryptoki, two larger and cross component features related to DASD disks, and more. Frank's blog post gets into further details and highlights, and instructions for how to download the latest ISO.